In [11]: pd.to_datetime(pd.Series(['05/23/2005'])) Out[11]: 0 2005-05-23 00:00:00 dtype: datetime64[ns]
In [12]: pd.to_datetime(pd.Series(['05/23/2005']), format="%m/%d/%Y") Out[12]: 0 2005-05-23 dtype: datetime64[ns]